Porous electrospun fiber and preparation method thereof

ABSTRACT

The present invention relates to a porous electrospun fiber with uniform minute pores and very large surface area, and thus porous electrospun fiber can be preferably applicable to various uses that need mesoporous materials, and a method of preparing the same. The porous electrospun fiber comprises an acrylamide-based polymer.

This application is a National Stage Entry of International ApplicationNo. PCT/KR2011/006334, filed Aug. 26, 2011, and claims the benefit ofKorean Patent Application No. 10-2010-0107070, filed on Oct. 29, 2010,all of which are hereby incorporated by reference in their entirety forall purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a porous electrospun fiber and apreparation method thereof, and more particularly, to a porouselectrospun fiber and a preparation method thereof that can be usedpreferably for various applications because of the uniform minute poresand very large surface area of the electrospun fiber.

BACKGROUND ART

The electro-spinning method is to prepare a fiber using electrostaticforce. The method has not been focused for a long time but has beenactively researched from recent decade in industrial separator material,tissue engineering and biological fields such as biomaterial scaffold,drug carrier or biosensor [Polymer Int'l, 2008, 57, 385-389;Biomaterials, 2008, 29, 1989-2006; Polymer, 2008, 49, 2387-2425;Polymer, 1999, 40, 4585-4592].

The electro-spinning method is to prepare a fiber using the interactionbetween surface tension and an electrostatic repulsion of electricalcharge which is driven in a liquid, when a sufficiently high voltage isapplied to a liquid droplet. Compared with convention dry melt spinningand wet spinning, it has simple mechanism and using method relatively,and has advantage of production for a fiber with various diameter suchas several nm to tens nm.

Generally, the electrospun fiber has large surface area per unit volumedue to relatively small diameter and good mechanical properties, thesurface of fiber can be modified with specific functional group, and thefiber can be used for easily preparing non-woven fabric with two orthree dimensional structure of minute pores having a diameter of severalmicrometer or less [Composites Science and Technology, 2003, 63,2223-2253; J. Biomater. Sci. Polym. Edu. 2006, 17, 1039-1056; 2010,13(1), 32-50].

Because of such advantages, the electrospun fiber is expected to be usedfor new materials for next-generation in various technical fields, forexamples, a biomaterial scaffold required for cell generation of bloodvessel, bone, ligament and the like [Int'l J. Biolog. Macromol., 2009,45, 504-510], a drug carrier [Acta Biomaterialia, 2010, 6, 102-109;Annu. Rev. Mater. Res., 2006, 36, 333-368; Current PharmaceuticalDesign, 2006, 12, 4751-4770; PCT WO 2009/078924], highly-efficientfilter material such as HEPA filter (high efficiency particulate airfilter) or ULPA filter (ultra low penetration air filter) [Journal ofIndustrial Textiles, 2007, 37, 151; Current Applied Physics, 2006, 6,1030-1035].

However, the kinds of fiber which can be prepared by theelectro-spinning method are very limited. Furthermore, the various fieldwhere the electrospun fiber is expected to be applied requires a porousmaterial, but the development of materials capable of be applied for thefield is still insignificant until now.

DISCLOSURE Technical Problem

Accordingly, the present invention provides a porous electrospun fiberhaving uniform minute pores and large surface area, thereby beingapplicable to a wide variety of fields and uses.

Further, the present invention provides a method for preparing a porouselectrospun fiber.

Technical Solution

The present invention provides a porous electrospun fiber comprising anacrylamide-based polymer comprising at least one repeating unitrepresented by Chemical Formula 1:

In Chemical Formula 1,

n is an integer of 15 to 1,800,

R is hydrogen or methyl; and

R′ is X,

wherein X is —Z—R″; Y is alkylene having 1 to 10 carbon atoms; Z isarylene having 6 to 20 carbon atoms; and R″ is a linear or branchedhydrocarbon having 10 to 20 carbon atoms, or a linear or branchedperfluorohydrocarbon having 10 to 20 carbon atoms.

In addition, the present invention provides a method of preparing aporous electrospun fiber comprising the steps of: dissolving anacrylamide-based polymer comprising at least one repeating unitrepresented by Chemical Formula 1 in an organic solvent to obtain apolymer solution: and performing electrospinning the polymer solution.

Hereinafter, the porous electrospun fiber and the preparation methodthereof according to the embodiment of the invention are described inmore detail.

According to an embodiment of the invention, a porous electrospun fibercomprising an acrylamide-based polymer comprising at least one repeatingunit represented by Chemical Formula 1 is provided:

In Chemical Formula 1,

n is an integer of 15 to 1,800,

R is hydrogen or methyl; and

R′ is X,

wherein X is —Z—R″; Y is alkylene having 1 to 10 carbon atoms; Z isarylene having 6 to 20 carbon atoms; and R″ is a linear or branchedhydrocarbon having 10 to 20 carbon atoms, or a linear or branchedperfluorohydrocarbon having 10 to 20 carbon atoms.

The present inventors found that a electrospun fiber comprising anacrylamide-based polymer includes a plurality of uniform micropores onits surface and has very high surface area, thereby being used forvarious applications in need of porous material such as a use ofselectively absorbing or entrapping volatile organic compounds, gaseousmolecule, organic material and protein and other uses for various potentuses, and completed the present invention.

The cause of porosity and large surface area of the electrospun fiberwill be described hereinafter.

Firstly, the properties of electrospun fiber may be caused by theacrylamide-based polymer. The acrylamide-based polymer is prepared by anacrylamide-based monomer (hereinafter, the monomer of the followingformula 2) through specific radical polymerization, for example RAFTpolymerization, and the polymer can have a plurality of mesoporeswithout additional treating step.

The acrylamide-based monomer has a chemical structure that contains aself-assembling non-polar aliphatic hydrocarbon (having more than 10carbon atoms), an arylene group causing π-π orbital interactions and anamide group causing intermolecular or intramolecular hydrogen bonding.Through the self-assembling behavior of the long-chain aliphatichydrocarbon, π-π orbital interactions of the arylene groups andintramolecular hydrogen bonding of the amide groups, the monomer canform a regular monoclinic crystal structure, preferably monoclinicsingle crystals in the solid state.

As the specific radical polymerization is carried out on the monomer, aleaving radical polymerization occurs with the monomer moleculeswell-oriented, and thereby the individual monomer molecules areregularly arranged in the polymer chain. More specifically, the monomermolecules well-oriented through the polymerization combine together toform a polymer chain (i.e., one polymer building block), and thesepolymer building blocks aggregate to form a regularly arranged polymer.Due to the regular arrangement of the polymer building blocks in thepolymer, the acrylamide-based mesoporous polymer can include a largenumber of mesopores having a uniform pore size without a separatetreatment after the polymerization reaction. For the same reason, theacrylamide-based mesoporous polymer can exhibit crystallinity.

As the fiber comprises acrylamide-based polymer having mesoporosity andcrystallinity, the electrospun fiber prepared from the polymer accordingto an embodiment of the invention shows a porosity including a pluralityof uniform minute pores on the surface. Furthermore, the process ofelectro-spinning the mesoporous polymer can make the pore size formed onthe surface be larger and increase the porosity.

In addition, in the process of electro-spinning the mesoporous polymer,the surface area of the polymer may be increased at 10 times, and thusthe electrospun fiber shows very large surface area and porosity.Particularly, the surface area and porosity of the electrospun isincreased still higher than those of the known material and electrospunfiber, and according to the present inventor's confirmation, theelectrospun fiber cannot form bead nearly, and has uniform surfacestate. Accordingly, the electrospun fiber of the embodiment can beapplied for various applications requiring the porous material or beingused by electrospun fiber.

Hereinafter, the acrylamide-based polymer and the electrospun fibercomprising the polymer will be described in more detail.

In the acrylamide-based polymer used for electrospun fiber as a maincomponent, Z is C6 to C20 arylene, and more specifically, can be

and the like.

R″ is a linear or branched hydrocarbon substituted at the ortho-, meta-or para-position of the aromatic ring in Z, and the hydrocarbon has along chain containing at least 10 carbon atoms, more specifically, 10 to20 carbon atoms. Also, the hydrocarbon of R″ may be substituted withFluorine and be a linear or branched perfluorohydrocarbon having 10 to20 carbon atoms.

The repeating unit of the above formula 1 and the monomer of the formula2 given below have such a long-chain hydrocarbon and arylene, so thepolymer more prominently exhibits such features as mesoporosity andcrystallinity.

The polymer may be a homopolymer consisting of one repeating unit offormula 1, or a copolymer comprising at least two repeating units offormula 1.

The acrylamide-based mesoporous polymer includes a large number of poreshaving a diameter of about 2.0 to 10.0 nm, preferably about 2.0 to 6.0nm, in the solid state. The term “diameter” of the pore as used hereinis defined as the length of the longest straight line between two pointson the circle, oval or polygon that is the cross-section in each pore.The polymer includes a large number of uniform pores in such a diameterrange, and hence the electrospun fiber comprising the polymer can alsoinclude a plurality of minute pores.

The polymer has a number-average molecular weight of about 5000 to500000, preferably about 7000 to 300000. The polymer is a crystallinepolymer having a melting point (T_(m)) of about 200 to 300° C.,preferably about 220 to 280° C. Due to the melting point and themolecular weight in the ranges, the polymer can be excellent in thermalstability pertaining to high melting point and high molecular weight,easily produced in the fiber form simply by spinning or the like, andalso maintaining its excellent mechanical properties such as strength.

From the structural analysis on the solid polymer using SAXS (SmallAngle X-ray Scattering) and WAXS (Wide Angle X-ray Scattering), and thethermal analysis on the phase-transition temperature of the polymer byDSC (Differential Scanning calorimetry), the inventors of the presentinvention found out that the acrylamide-based polymer may be acrystalline polymer having a melting point in the above-mentioned range.Unlike the conventional polymers of up-to-date known similar structures,the polymer of the embodiment has mesoporosity and crystallinity, andthe electrospun fiber comprising the polymer can have the propertiessuch as porosity different from those of the other conventionalmaterials.

The inventors of the present invention also found out that the porediameter on the polymer decreased with an increase in the annealingtemperature during an annealing which was carried out on the polymer inthe temperature range of at least about 200° C. and below the meltingtemperature, for example, between about 220° C. and 240° C. As theannealing temperature increased, the pore diameter decreased by about0.4 to 0.7 nm, more specifically, by about 0.5 to 0.6 nm.

It was also revealed that the pore diameter on the polymer increasedwith a change in the chemical structure of R′ bonded to the amide(—CO—NH—) group in the repeating unit of formula 1, or with an increasein the length of the aliphatic hydrocarbon bonded to the end of R′,i.e., an increase in the number of carbon atoms of R″. For example, thepore diameter increased by about 0.1 to 1.0 nm, more specifically, byabout 0.2 to 0.7 nm as the number of carbon atoms increased from 12 to16. The pore diameter also increased as the chemical structure of Z inR′ changed from phenylene into another different aromatic structure suchas naphthalene or anthracene.

The reason of the change in the pore diameter presumably lies in thatthe mesoporous three-dimensional structure (or, crystal structure) ofthe polymer changes by annealing process, by the changed chemicalstructure of R′ bonded to the amide group, or by a change in the numberof carbon atoms of R″ bonded to the end of R′. This can be supported bythe results of the DSC thermal analysis.

The pore size of polymer can be controlled easily by heat treatment,modification of functional group or the adjustment of hydrocarbon chainlength in amide group of the repeating unit. Also, the pore size ofelectrospun fiber comprising the polymer can be controlled easily. Thus,the electrospun fiber can be used preferably for various applicationsrequiring the porous material.

Because the electrospun fiber of an embodiment of the inventioncomprises novel polymer having mesoporosity and crystallinity,specifically the acrylamide-based polymer, diameter size, porosity anduniform pores formed on the surface which has not been reported beforecan be achieved. The electrospun fiber and the non-woven fabriccomprising the electrospun fiber can be can be preferably used in thoseapplications that need mesoporous materials.

More specifically, the porous electrospun fiber has a diameter of about200 nm to 10 μm, and preferably about 250 nm to 7 μm. The term“diameter” of electrospun fiber as used herein is defined as the lengthof the longest straight line between two points on the circle, oval orpolygon that is the cross-section in each fiber. The diameter ofelectrospun fiber can be controlled by the condition ofelectro-spinning, or the kinds of repeating unit and molecular weight ofpolymer. The electrospun fiber has various diameters within the ranges.

A plurality of pores on the surface of electrospun fiber can be formedin a diameter of about 20 to 500 nm, preferably about 50 to 450 nm, andmore preferably about 100 to 400 nm, and the pore can be distributeduniformly on the surface of fiber.

As described above, the porosity of electrospun fiber is derived fromthe mesoporosity of acrylamide-based polymer, and increases more in theelectro-spinning process, thereby providing the fiber with the pluralityof uniform pore having the range of pore size. The porosity ofelectrospun fiber can make the fiber be wider variety of applications.In addition, the pore size of the electrospun fiber can be controlled bythe methods as described above, and thus porosity of electrospun fibercan make the fiber be preferably used in those applications that needmesoporous materials

Meanwhile, according to an embodiment of the invention, the method ofpreparing the electrospun fiber is provided. The method can comprise thesteps of dissolving an acrylamide-based polymer comprising at least onerepeating unit represented by Chemical Formula 1 in an organic solventto obtain a polymer solution: and performing electrospinning the polymersolution.

According to the method, the polymer solution is electrospun afterobtaining the acrylamide-based polymer, thereby providing theelectrospun fiber with the described properties. Hereinafter, theacrylamide-based polymer and the electrospun fiber comprisingacrylamide-based polymer will be explained in more detail.

Firstly, the acrylamide-based polymer can be prepared by performing theRAFT polymerization for the reactants containing at least one monomerrepresented by Chemical Formula 2, in the presence of radical initiator,and optionally the RAFT (reverse addition fragmentation transfer) agent;and precipitating the polymerization product in non-solvent:

wherein R and R′ are as defined above.

The acrylamide-based monomer having a specified chemical structure offormula 2 is subjected to RAFT polymerization under specified conditionsand then to precipitation in a nonsolvent to easily form theacrylamide-based mesoporous polymer having mesoporosity andcrystallinity. The reason that the polymer prepared by this method hasmesoporosity and crystallinity is already described enough and will notbe mentioned hereinafter in any further detail.

It is therefore possible to prepare a mesoporous polymer having a largenumber of pores in a uniform pore size merely by a polymerizationprocess alone without any other separate chemical treatment.

The preparation method may further comprise, prior to the polymerizationstep, preparing a reaction solution including the radical initiator, theRAFT agent, and the reactant; adding the reaction solution in apolymerization ampoule and eliminating oxygen by a freeze-thaw method;and sealing the ampoule. In this manner that the individual reactantsand the initiator are added in the oxygen-free polymerization ampouleand then subjected to polymerization, the RAFT polymerization well-knownas a kind of leaving radical polymerization takes place more adequatelyto form the acrylamide-based mesoporous polymer with a highpolymerization conversion.

The preparation method may further comprise, after the precipitationstep, dissolving the precipitated polymer product in an organic solvent;and re-precipitating the polymer product solution with a nonsolvent. Theaddition of the re-precipitation step helps the preparation of theacrylamide-based mesoporous polymer having crystallinity in a morepreferable way.

In the preparation method, the monomer is any acrylamide-based monomerof formula 2 and may include, for example, N-(p-dodecyl)phenylacrylamide (DOPAM), N-(p-tetradecyl)phenyl acrylamide (TEPAM),N-(p-hexadecyl)phenyl acrylamide (HEPAM), N-(p-dodecyl)naphthylacrylamide (DONAM), N-(p-tetradecyl)naphthyl acrylamide (TENAM),N-(p-hexadecyl)naphthyl acrylamide (HENAM), N-(p-dodecyl)azobenzenylacrylamide (DOAZAM), N-(-p-tetradecyl)azobenzenyl acrylamide (TEAZAM),N-(p-hexadecyl)azobenzenyl acrylamide (HEAZAM), orN-[4-(3-(5-(4-dodecyl-phenylcarbamoyl)pentyl-carbamoyl)-propyl)phenylacrylamide (DOPPPAM). Of course, the monomer may be a mixture of atleast two of those listed monomers.

The monomer may be a monoclinic crystal structure, preferably in theform of monoclinic single crystal, which can be supported by thefollowing examples. As the monomer is obtained in the form of monoclinicsingle crystal and then subjected to RAFT polymerization to prepare apolymer, the individual monomer molecules in the polymer chain are moreregularly arranged and better oriented to combine together and therebymore preferably form the polymer having mesoporosity and crystallinity.

To obtain the monomer in the form of single crystal, a crystal growthagent is added in a polar solvent and/or a nonpolar solvent after thesynthesis of the monomer, to grow single crystals. The growth rate ofthe single crystal depends on the crystal growth time and temperature,or the chemical structure and concentration of the added crystal growthagent (e.g., seed crystal).

The radical initiator, the RAFT agent, and the monomer are dissolved inan organic solvent to prepare a reaction solution, and RAFTpolymerization takes place in the reaction solution. The organic solventas used herein includes at least one non-polar solvent selected from thegroup consisting of n-hexane, cyclohexane, benzene, toluene,chlorobenzene, dichlorobenzene, methylene chloride, or1,2-dichloroethane; or at least one polar solvent selected from thegroup consisting of acetone, chloroform, tetrahydrofuran (THF), dioxane,monoglyme, diglyme, dimethylformamide (DMF), dimethylsulfoxide (DMSO),or dimethylacetamide (DMAC). The organic solvent may also be a mixtureof the non-polar and polar solvents. The organic solvent can also beused in the re-precipitation step to dissolve the polymer product.

In the reaction solution, the monomer is dissolved in the organicsolvent at a concentration of about 3.0 to 50 wt %, preferably about 5.0to 40 wt % with respect to the weight of the organic solvent. Thereaction solution in this concentration range makes the subsequentpolymerization process work out in an efficient way.

The radical initiator used along with the monomer may be any knowninitiator for radical polymerization without limitation, including anyone selected from the group consisting of azobisisobutyronitrile (AIBN),2,2′-azobis-2,4-dimethylvaleronitrile, benzoyl peroxide (BPO), ordi-t-butyl peroxide (DTBP); and at least two selected from the group ofradical initiators.

The RAFT agent as used herein includes any thermal decompositioninitiator such as S-1-dodecyl-S′-(α,α′-dimethyl-α″-aceticacid)trithiocarbonate, cyanoisopropyl dithiobenzoate,cumyldithiobenzoate, cumylphenylthioacetate,1-phenylethyl-1-phenyldithioacetate, or4-cyano-4-(thiobenzoylthio)-N-succinimide valerate. The RAFT agent mayalso be a mixture of at least two of the above-listed initiators.

The radical initiator and the RAFT agent are used at a concentration ofabout 0.001 to 5.0 wt % with respect to the weight of the monomer.

In the above-described preparation method, the RAFT polymerization stepis carried out at a reaction temperature of about 60 to 140° C., forabout 30 to 200 hours, more specifically, about 50 to 170 hours.

In the precipitation or re-precipitation step of the preparation method,the nonsolvent is a solvent that does not dissolve the product of thepolymerization process or the acrylamide-based mesoporous polymer. Theexamples of the nonsolvent may include a polar solvent such as methanol,ethanol, n-propanol, isopropanol, or ethyleneglycol; or a non-polarsolvent such as n-hexane, cyclohexane, or n-heptane. Of course, thenonsolvent may also be a mixture of at least two of the above-listedsolvents. The precipitation and re-precipitation processes using thenonsolvent facilitate the production of the polymer having mesoporosityand crystallinity with a high purity.

After preparing the acrylamide-based polymer according to the abovemethod, the product is dissolved in an organic solution to produce thepolymer solution to be used for electro-spinning.

The solvent used for dissolving the polymer can be any being capable ofdissolving the polymer. For examples, the solvent may comprise at leastone nonpolar solvent selected from the group consisting of n-hexane,cyclohexane, benzene, toluene, chlorobenzene, dichlorobenzene,methylenechloride and 1,-dichloroethan; or at least one polar solventselected from the group consisting of acetone, chloroform,tetrahydrofuran (THF), dioxane, monoglyme, diglyme, dimethylformamide(DMF), dimethylsulphoxide (DMSO) and dimethylacetamide (DMAC). A mixedsolvent including at least two solvents selected from the non-polarsolvents or polar solvents, or a mixed solvent including the non-polarsolvent and the polar solvent can be used. When the mixed solvent isused, the polar solvent is preferably contained in an amount of about60-90 wt % based on the total mixed solvent. In the polymer solution,the polymer is preferably dissolved in the solvent at an amount of about10 to 40 wt %.

The kind and concentration of the solvent can be selected depending onthe chemical structure and molecular weight of the acrylamide-basedpolymer.

After preparing the polymer solution, the electrospun fiber can beformed by carrying out the electro-spinning the solution. The chemicalor physical properties of the electrospun fiber can be affected by themolecular structure, morphological structure and molecular weight ofused polymer, the kind and concentration of solvent, the spinning speed(mL/min) of polymer solution, voltage applied for the electro-spinningdevice, the diameter of spinning needle, the distance between the needleand fiber collector and the like.

In these aspects, to prepare the electrospun fiber having more uniformpore size and diameter, the electro-spinning may be carried out byapplying about 10 to 30 kV preferably. The electro-spinning deviceincludes a nozzle with a diameter of about 20 to 30 gauge where thedistance between nozzle and the collector is preferably about 10 to 20cm.

In addition, the spinning speed may be dependent on the kind andmolecular weight of polymer, and the kind and concentration of solvent,and for example, the spinning speed may be preferably about 5 to 20mL/min, in order to prepare the uniform electrospun fiber that shows theproperties and does not form bead.

According to the method, the electrospun fiber having the porosity andlarge surface area can be prepared, and the electrospun fiber can beused for various applications of possible electrospun fiber and requiredfor porous material.

Advantageous Effects

As described above, the present invention provides an electrospun fibercomprising an acrylamide-base mesoporous polymer and its preparationmethod. The electrospun fiber has large surface area and the porositythat a plurality of uniform pore size on the surface, and thus can beused for various applications of possible electrospun fiber and requiredfor porous material

For example, the electrospun fiber can be used for adsorbing variousorganic compounds, for drug carrier and filter in industrial field.

DESCRIPTION OF DRAWINGS

FIG. 1 shows the X-ray diffraction pattern of a DOPPPAM crystal obtainedin Example 3.

FIG. 2 shows the DSC thermal analysis curve of a polymer prepared inExample 4.

FIG. 3 shows the TEM picture of a thin film including the polymer ofExample 4.

FIG. 4 shows the SEM picture of electrospun fiber obtained in Example11.

FIG. 5 shows the SEM picture of electrospun fiber obtained in Example 12

FIG. 6 shows the SEM picture of electrospun fiber obtained in Example 13

FIGS. 7a and 7b shows the SEM picture of electrospun fiber obtained inExample 14

FIG. 8 shows the SEM picture of electrospun fiber obtained in Example15.

FIG. 9 shows the SEM picture of electrospun fiber obtained in Example 16

FIG. 10 shows the SEM picture of electrospun fiber obtained in Example17

MODE OF INVENTION

In the following are set forth specific examples according to theinvention, describing the function and effect of the invention infurther detail. It is to be understood that the examples are only forillustrative purposes and are not intended to limit the scope of theinvention.

Examples 1, 2 and 3 Synthesis of Acrylamide-Based Monomer andDetermination of Crystallinity Example 1 Synthesis ofp-Dodecylphenylacrylamide (DOPAM) and Preparation of Single Crystal

Firstly, p-dodecylaniline (12 g, 0.046 mol) was dissolved in THF solvent(100 mL). The solution was poured into a 100 mL three-mouthed roundflask, and an acid eliminator was added dropwise through a funnel for 10minutes, where the acid eliminator contained imidazole and triethylamine at the same mole fraction (0.023 mol). Under the nitrogenatmosphere, a solution containing acryloyl chloride (3.8 mL, 0.047 mol)in THF (20 mL) was gradually added dropwise to the mixed solutionthrough a dropping funnel for 20 minutes. Meanwhile, the solution wascooled on ice bath to prevent the temperature of the reaction mixturefrom rising above 5° C. After 6 hours of reaction at 0° C., the solutionwas kept at 25° C. for more 9 hours of reaction. Upon completion of thereaction, the solution was passed through a filter paper to eliminateprecipitated salts, and the solvent was evaporated from the filtrate onan evaporator. The solid thus obtained was dissolved in dichloromethane(100 mL) and added to a separatory funnel along with 10% aqueous NaHCO₃solution (50 mL). The funnel was shaken vigorously and set aside toallow for the complete separation of the aqueous phase and thereby toremove unreacted acryloyl chloride. Magnesium sulfate (1.0 g) was addedto the separated dichloromethane solution. After stirred for 5 hours,the solution was subjected to filtration to remove a trace amount ofwater dissolved in the solvent. The dichloromethane solution thusobtained was kept on the evaporator, and n-hexane (100 mL) was added.The solution was stirred for 2 hours, and unreacted p-dodecyl anilinewas filtered out from the solution. The filtrate was then removed of thesolvent on the evaporator to yield a white solid DOPAM product (yield95%). The chemical structure of the DOPAM product was identified byhydrogen nuclear magnetic resonance (¹H-NMR) spectrum. The results wereas follows.

¹H-NMR(CDCl₃): e, 7.5 (d, 2H); d, 7.2 (s, 1H); f, 7.15 (d, 2H); b, 6.4(d, 1H); c, 6.2 (q, 1H); b, 5.8 (d, 1H); g, 2.6 (t, 2H); h, 1.25-1.35(m, 20H); i, 0.935 (t, 3H).

The DOPAM product (T_(m)=101° C.) was purified by re-crystallizationwith ethanol three times. The purified DOPAM was added to THF solvent,an several drops of a non-polar solvent was added. The solution was keptbelow −10° C. for a defined period of time to grow single crystals ofthe monomer.

It turned out that the growth rate of the single crystals was dependenton the composition and proportion of polar and non-polar solvents,crystal growth time and temperature, and the structure and concentrationof the crystal growth agent added.

XRD (X-Ray Diffractometry) was used to identify the crystal structure ofthe single crystals obtained in Example 1. The crystallographic datathus obtained is presented in Table 1, which shows that the singlecrystals of the monomer of Example 1 have a monoclinic crystalstructure.

TABLE 1 Crystallographic Data for Single Crystals of Monomer of Example1 Empirical Formula C₂₁H₃₃N₁O₁ Formula weight 315.48 Temperature [K]293(2) K Wavelength [Å] 0.71073 Crystal system, space group Monoclinic,P2₁/c a [Å] 4.7055(13) b [Å] 43.315(16) c [Å] 9.4150(19) β [°]95.158(19) Volume [Å³] 1911.2(10) d_(calcd) [gcm⁻³] 1.096 μ [mm⁻¹] 0.066F(000) 696 Crystal size [mm] 0.55 × 0.30 × 0.25 θ Range[°] 1.88-26.33Data/parameters 1845/213 GOF on F² 1.111 R1, wR2 [I > 2σ(I)] 0.0975,0.2551 Largest diff. peak and hole [e.Å⁻³] 0.358 and −0.343

Example 2 Synthesis of p-Tetradecylphenylacrylamide (TEPAM) andp-hexadecylphenylacrylamide (HEPAM) and Preparation of Single Crystal

TEPAM and HEPAM were synthesized with the yields of 90% and 93%,respectively in the same manner as described in Example 1, exceptingthat p-tetradecylaniline having 14 carbon atoms or p-hexadecylanilinehaving 16 carbon atoms was used instead of p-dodecylaniline having 12carbon atoms. The single crystals of TEPAM and HEPAM were grown andidentified through XRD analysis technique in the same manner asdescribed in Example 1, revealing that the single crystals had amonoclinic crystal structure.

Example 3 Synthesis ofN-[4-(3-(5-(4-dodecyl-phenylcarbamoyl)pentyl-carbamoyl)-propyl)phenylacrylamide (DOPPPAM) and Preparation of Single Crystal

4-(4-aminophenyl)butyric acid (6 g, 3.36 mmol) was added to a 200 mLthree-mouthed round flask, and methylene chloride (100 mL) was added anddissolved under the nitrogen atmosphere at 40° C. To the solution wasadded chlorotrimethyl silane (6.0 mL). The solution was refluxed andagitated for 2 hours and, after reaction, cooled down to the roomtemperature. While kept at 0 to 5° C. on an ice bath under the nitrogenatmosphere, an acid eliminator (in an excess amount by 10% inconcentration relative to the reactant) was added dropwise through afunnel for 10 minutes, where the acid eliminator contained imidazole andtetraethyl amine mixed at the same mole fraction. In the same manner, asolution containing acryloyl chloride (2.8 mL) in methylene chloride (30mL) was added dropwise for 20 minutes, and the solution was kept for 30minutes of reaction and then warmed up to the room temperature for 2more hours of reaction. After the solvent was removed, 2M sodiumhydroxide solution (200 mL) was added, and the solution was stirred for2 hours. The aqueous solution was weak-acidified (pH 5˜6) with a 2Mhydrogen chloride solution to form an aqueous solution containing awhite precipitate. This solution was added to a separatory funnel alongwith ethylacetate (200 mL) and shaken up to cause phase separation intoaqueous and ethylacetate layers. The solvent in the ethylacetate layerwhere the product is dissolved was removed on an evaporator, and theresidual solid was dried out in a vacuum oven for 24 hours to yield awhite 4-(4-acrylaminophenyl)butyric acid (APB) solid (yield 92%). Themelting point of the solid was 107° C.

Subsequently, N-(t-butylester)caproic acid (6.0 g, 25.1 mmol) and4-dodecylamine (5.1 g) were added to a 500 mL three-mouthed round flask,and THF (300 mL) was added and dissolved at 0˜5° C. on an ice bath underthe nitrogen atmosphere. DMAP (1.59 g, 12.9 mmol) was added as acatalyst, and the solution was stirred for 10 minutes. EDC (5.98 g, 31.2mmol) was added as a moisture remover, and the solution was stirred forone hour and then 18 more hours at the room temperature. After thereaction, the solution was precipitated in distilled water (1200 mL) andstirred for one hour. The residual substances, such as DMAP, EDC, EDCurea salt and THF were filtered out, and a reactant-product mixture wasthen extracted. An aqueous NaHCO₃ solution (200 mL) was added threetimes to the extracted mixture, and the solution was stirred for onehour and removed of unreacted N-(t-butylester)caproic acid throughfiltration. To the solid obtained was added n-hexane (600 mL), and thesolution was stirred for one hour and removed of unreacted4-dodecylaniline through filtration. The residual solid was dried out ina vacuum oven for 24 hours to yield a white5-(4-dodecylphenyl-carbamoyl)pentyl)-carbamic acid t-butyl ester solid(yield 91%).

The solid product, 5-(4-dodecylphenyl-carbamoyl)pentyl)-carbamic acidt-butyl ester (6.0 g, 12.6 mmol) was added to a one-mouthed round flask,and methylene chloride (150 mL) was added and dissolved at the roomtemperature. Trifluoroacetic acid (18.9 mL, 2.52 mol) was added, and thesolution was stirred for 2 hours and removed of the solvent. Ethylether(90 mL) was added, and the solution was stirred for 30 minutes and thenremoved of unreacted 5-(4-dodecylphenyl-carbamoyl)pentyl)-carbamic acidt-butyl ester through filtration. The residual solid was dried out in avacuum oven for 24 hours to yield a white5-(4-dodecylphenyl-carbamoyl)pentyl)-amine solid (yield 97%).

The above 5-(4-dodecylphenyl-carbamoyl)pentyl)-amine solid (3.0 g, 7.9mmol) and the APB solid (1.86 g) previously obtained were added to a 500mL three-mouthed round flask, and THF (150 mL) was added and dissolvedat 0˜5° C. on an ice bath under the nitrogen atmosphere. DMAP (1.95 g,10.1 mmol) was added as a catalyst, and the solution was stirred for 10minutes. EDC (1.831 g, 9.6 mmol) was added as a moisture remover, andthe solution was stirred for one hour and then 18 more hours at the roomtemperature. After the reaction, the solution was precipitated indistilled water (600 mL) and stirred for one hour. The residualsubstances, such as DMAP, EDC, EDC urea salt and THF were filtered out,and a reactant-product mixture was then extracted. An aqueous NaHCO₃solution (600 mL) was added to the extracted mixture, and the solutionwas stirred for one hour and removed of unreacted ABP throughfiltration. To the solid thus obtained was added ethanol (300 mL), andthe solution was stirred for one hour and removed of unreacted5-(4-dodecylphenyl-carbamoyl)pentyl)-amine through filtration. Theresidual solid was dried out in a vacuum oven for 24 hours to yield awhite DOPPPAM solid (yield 89%, melting point 174° C.).

The DOPPPAM thus obtained was dissolved in THF solvent, and severaldrops of a non-polar solvent were added. To the solution was added atrace of a crystal growth agent to cause crystal growth at a lowtemperature below −10° C. for a defined period of time, therebyproducing pure needle-like DOPPPAM crystals. The chemical structure ofthe pure DOPPPAM was identified by hydrogen nuclear magnetic resonance(¹H-NMR) spectrum. The results were as follows.

¹H-NMR (DMSO-d6): 4, 10.06 (s, 1H); 14, 9.76 (s, 1H); 10, 7.78 (m, 1H);5, 7.59 (m, 2H); 6, 7.23 (m, 2H); 15, 7.12 (d, 2H); 16, 7.08 (d, 2H); 1,6.42 (q, 1H); 2, 6.24 (d, 1H); 3, 5.72 (d, 1H); 11, 3.01 (m, 2H); 7,2.26 (m, 2H); 9, 2.06 (m, 2H); 8, 1.78 (m, 2H); 13, 1.55 (m, 2H); 17,1.52 (m, 2H); 12, 1.40 (m, 6H); 17, 1.23 (m, 20H); 18, 0.85 (t, 3H)

The XRD instrument was used to determine the crystallinity of theneedle-like DOPPPAM crystals obtained in Example 3. The X-raydiffraction pattern of the crystals is shown in FIG. 2, whichdemonstrates that the DOPPPAM also had crystallinity. According to theX-ray diffraction pattern, the monomer of Example 3 also turned out tohave a crystal structure in which the individual molecules were verywell-arranged spatially in the solid state.

Examples 4-10 Preparation of Novel Acrylamide-Based Mesoporous PolymerExample 4 Preparation of Poly(DOPAM)-1

The DOPAM monomer (1.0 g) obtained the rod-like crystal form in Example1 was dissolved in THF (6.3 mL) and poured in a 10 mL Schenk flask alongwith cyanoisopropyl dithiobenzoate (1.75 mg) as a RAFT agent and AIBN(0.87 mg) as a radical initiator. The solution was stirred under thenitrogen atmosphere for 30 minutes, removed of oxygen and kept in asilicon oil container at 70° C. to cause RAFT polymerization for 72hours. After the polymerization reaction, the reaction solution wasprecipitated with methanol (200 mL) and then subjected to filtration togive an orange solid. The solid was dissolved in THF (8 mL) andre-precipitated with an excess of methanol. The light yellowish solidthus obtained was dried out in a vacuum oven for 24 hours to yield apure homopolymer, Poly[DOPAM]-1 represented by Chemical Formula 3. Thepolymerization conversion and the number-average molecular weight were48% and 14900, respectively. The homopolymer had a very narrow molecularweight distribution of 1.25 and a melting point (T_(m)) of 241° C.

Example 5 Preparation of Poly(DOPAM)-2

The procedures were performed to obtain a pure Poly[DOPAM]-2 polymer inthe same manner as described in Example 4, excepting that there wereused the DOPAM monomer (1.5 g) obtained in the rod-like crystal form inExample 1, benzene (7.8 mL), cyanoisopropyl dithiobenzoate (2.63 mg) asa RAFT agent and AIBN (1.3 mg) as a radical initiator. Thepolymerization conversion and the number-average molecular weight were66% and 35000, respectively. The polymer had a very narrow molecularweight distribution of 1.39 and a melting point (T_(m)) of 242° C.

Example 6 Preparation of Poly(DOPAM)-3

The DOPAM monomer (1.0 g) obtained in the rod-like crystal form inExample 1, mixture 6.5 mL of THF/benzene (mixing volume ratio of 30/70),and BPO (10 mg) as a radical initiator were poured in a 20 mL ampouleand then the oxygen of the solution was removed by freeze-thaw method.The ampoule was sealed and kept at 80° C. in an oven to cause RAFTpolymerization for 48 hours. After the polymerization reaction, thereaction solution was precipitated with methanol (30 mL) and thensubjected to filtration to give a light yellowish solid. The solid wasdissolved in 10 mL of THF and reprecipitated with excess methanol Thesolid was dried out in a vacuum oven for at least 24 hours to yield apure homopolymer, Poly(DOPAM)-3. The polymerization conversion and thenumber-average molecular weight were 94% and 99000, respectively. Thehomopolymer had a molecular weight distribution of 3.2 and a meltingpoint (T_(m)) of 242° C.

Example 7 Preparation of Poly(DOPAM)-4

The procedures were performed to obtain a pure Poly[DOPAM]-4 polymer inthe same manner as described in Example 6, excepting that there wereused the DOPAM monomer (1 g) obtained in the rod-like crystal form inExample 1, benzene (6.5 mL), BPO (10 mg) as a radical initiator andpolymerization time of 72 hours. The polymerization conversion and thenumber-average molecular weight were 97% and 115000, respectively. Thepolymer had a very narrow molecular weight distribution of 3.4 and amelting point (T_(m)) of 242° C.

Example 8 Preparation of Poly(TEPAM)

The procedures were performed to obtain a pure Poly[TEPAM] polymerrepresented by Chemical Formula 4 in the same manner as described inExample 7, excepting that there was used the TEPAM monomer (1.0 g)obtained in the rod-like crystal form in Example 2. The polymerizationconversion and the number-average molecular weight were 93% and 119100,respectively. The Poly[TEPAM] homopolymer had a very narrow molecularweight distribution of 2.7 and a melting point (T_(m)) of 242° C.

Example 9 Preparation of Poly(HEPAM)

The procedures were performed to obtain Poly[HEPAM] represented byChemical Formula 5 in the same manner as described in Example 7,excepting that there was used the HEPAM monomer (1.0 g) obtained in therod-like crystal form in Example 2. The polymerization conversion andthe number-average molecular weight were 86% and 61200, respectively.The Poly[HEPAM] homopolymer had a very narrow molecular weightdistribution of 2.4 and a melting point (T_(m)) of 241° C.

Example 10 Preparation of Poly(DOPPPAM)

The procedures were performed to obtain a light yellowish homopolymer,Poly[DOPPPAM] represented by Chemical Formula 6 in the same manner asdescribed in Example 7, excepting that there were used the DOPPPAMmonomer (1.0 g) obtained in the needle-like crystal form in Example 3,DMF (4.22 mL), and DTBP (0.002 mL) as a radical initiator and thatpolymerization was carried out at 110° C. (polymerization temperature)for 96 hours (polymerization time). The polymerization conversion andthe number-average molecular weight were 86% and 39200, respectively.The Poly[DOPPPAM] homopolymer had a very narrow molecular weightdistribution of 2.9 and a melting point (T_(m)) of 256° C.

Experimental Example Analysis on Thermal Properties and Solid Structureof Novel Acrylamide-Based Mesoporous Polymer

(1) Analysis on Thermal Properties of Polymer by DSC

A DSC thermoanalytical instrument was used to examine the phasetransition behavior of the Poly(DOPAM), Poly(TEPAM) and Poly(HEPAM)polymers prepared in Examples 4, 8 and 9, respectively. Through the DSCthermoanalysis, the three polymers turned out to be crystalline polymerswith melting temperatures (T_(m)) of 241, 237 and 229° C., respectively.The melting temperature (T_(m)) of the polymers had a tendency to lowergradually with an increase in the number of carbon atoms of thealiphatic hydrocarbon introduced at the end in order of 12, 14 and 16.The Poly(DOPPPAM) polymers of Examples 10 of a different chemicalstructure also turned out to be a crystalline polymer having a meltingtemperature (T_(m)) of 256° C.

FIG. 2 is a DSC thermal analysis curve showing the behavior of the phasetransition temperature of Poly(DOPAM)-1 obtained in Example 4. Referringto FIG. 2, the melting temperature (T_(m)) of the mesoporous structureformed by the polymer chain of the Poly(DOPAM) polymer was 241° C. Themelting temperatures (T_(m)) of the minute crystals formed from thealiphatic hydrocarbon introduced at the end of the repeating unit wereabout 5° C. As the phase transition melting temperatures appeared in thealmost same temperature range on both heating and cooling curves withthe same heat capacity, the porous structure formed among the polymerchains of the Poly(DOPAM) polymer was presumably oriented in arelatively stable way. There was no significant difference in themelting temperature (T_(m)) when the Poly(DOPAM) polymer had anumber-average molecular weight greater than 8000.

(2) Analysis on Porous Structure of Polymer by TEM

A thin film including the polymer Poly(DOPAM)-1 of Example 4 was madeand taken to get the TEM (Transmission Electron Microscopy) image asshown in FIG. 3. The thin film was prepared in the manner that the solidpowder of Poly(DOPAM)-1 was annealed at the melting temperature for 6hours and quenched in liquid nitrogen. FIG. 3 is the TEM image of thethin film that was cut up in thickness about 50 to 120 nm and subjectedto deposition of RuO₄ vapor. Referring to FIG. 3, the dark part showsthe RuO₄ vapor deposited on the benzene group introduced in the polymerchain of Poly(DOPAM)-1 forming the frame of the cylindrical structure.It can be seen from FIG. 6 that the bright image structure with a poresize of about 3.5 nm is relatively uniformly distributed over thesurface of the thin film. In conclusion, the polymers of the Examplescontained a large number of mesopores with a uniform pore size.

Example 11-17 Preparation of Porous Electrospun Fiber from NovelMesoporous Acrylamide-Based Polymer Example 11

Poly(DOPAM)-3 (1.0 g) obtained Example 6 was dissolved in 5.1 mL of THFto produce the polymer solution with using electro-spinning device(ESR-200RD) (NanoNC). 5 mL of the polymer solution was poured into asyringe and was applied for electro-spinning device by using stainlessneedle having 25 gauge (diameter of 0.508 mm) under the condition ofapplied voltage of 15 kV, spinning speed of 15 mL/min, and the distanceof 12 cm between the needle and collector to produce electrospun fiber.SEM picture of electrospun fiber was shown in FIG. 4. The resultconfirmed that the electrospun fiber had a diameter of 250 to 450 nm,and uniformly-distributed pore of diameter 20 to 50 nm on its surface.

Example 12

The procedures were performed to obtain a electrospun fiber in the samemanner as described in Example 11, excepting that there were used themesoporous polymer Poly(DOPAM)-4 (1.0 g) prepared in Example 7, 2.9 mLof THF, and applied voltage of 10 kV. SEM picture of the electrospunfiber was shown in FIG. 5. The result confirmed that the electrospunfiber had a diameter of about 7 μm, and uniformly-distributed pore ofdiameter 70 to 400 nm on its surface.

Example 13

The procedures were performed to obtain a electrospun fiber in the samemanner as described in Example 1, excepting that there was used appliedvoltage of 15 kV. SEM picture of the electrospun fiber was shown in FIG.6. The result confirmed that the electrospun fiber had a diameter ofabout 6 μm, and uniformly-distributed pore of diameter 100 to 300 nm onits surface.

Example 14

The procedures were performed to obtain a electrospun fiber in the samemanner as described in Example 12, excepting that there were used 3.4 mLof THF, and applied voltage of 20 kV. SEM pictures of the electrospunfiber were shown in FIGS. 7a and 7b . The result confirmed that theelectrospun fiber had a diameter of about 2 μm, anduniformly-distributed pore of diameter 50 to 200 nm on its surface.

Example 15

The procedures were performed to obtain a electrospun fiber in the samemanner as described in Example 12, excepting that there were used themesoporous polymer Poly(TEPAM) (1.0 g) prepared in Example 8 and appliedvoltage of 10 kV. SEM picture of the electrospun fiber was shown in FIG.8. The result confirmed that the electrospun fiber had a diameter ofabout 4 to 7 μm, and uniformly-distributed pore of diameter 100 to 500nm on its surface.

Example 16

The procedures were performed to obtain a electrospun fiber in the samemanner as described in Example 12, excepting that there were used themesoporous polymer Poly(HEPAM) (1.0 g) prepared in Example 9 and appliedvoltage of 20 kV. SEM picture of the electrospun fiber was shown in FIG.9. The result confirmed that the electrospun fiber had a diameter ofabout 2 to 4 μm, and uniformly-distributed pore of diameter 100 to 250nm on its surface.

Example 17

The procedures were performed to obtain a electrospun fiber in the samemanner as described in Example 11, excepting that there were used themesoporous polymer Poly(DOPPPAM) (1.0 g) prepared in Example 10, 3.2 mLof DMF, and applied voltage of 15 kV. SEM picture of the electrospunfiber was shown in FIG. 10. The result confirmed that the electrospunfiber had a diameter of about 500 nm to 1.0 μm, anduniformly-distributed pore of diameter 40 to 80 nm on its surface.

Analysis of Electrospun Fiber

In the Example, the diameter and surface morphology of electrospun fiberwas analyzed by SEM (scanning electron microscope, Hitachi S-4800). TheSEM pictures are shown in FIGS. 4 to 10. More specifically, the polymersolution of each Example was electrospun directly to silicon wafer(silicon wafer, 2.0×2.0 cm) to obtain the electrospun fiber. Theelectrospun fiber was dried under the vacuum, and analyzed at 15.0 kVwith SEM.

Referring to the Examples and FIGS. 4 to 10, the electrospun fiber ofExamples 11 to 17 showed porosity that the uniformly-sized pores were onthe surface of electrospun fiber, and had large surface area with thecontrolled diameter without forming bead. Hence, the electrospun fibercan be preferably applicable to various uses that need mesoporousmaterials.

The invention claimed is:
 1. A porous electrospun fiber comprising an acrylamide-based polymer comprising at least one repeating unit represented by Chemical Formula 1:

In Chemical Formula 1, n is an integer of 15 to 1,800, R is hydrogen or methyl; and R′ is X,

wherein X is —Z—R″; Y is alkylene having 1 to 10 carbon atoms; Z is arylene having 6 to 20 carbon atoms; and R″ is a linear or branched hydrocarbon having 10 to 20 carbon atoms, or a linear or branched perfluorohydrocarbon having 10 to 20 carbon atoms.
 2. The porous electrospun fiber of claim 1, wherein the fiber has a diameter of 200 nm to 10 μm.
 3. The porous electrospun fiber of claim 1, wherein the fiber includes a plurality of pores having a diameter of 20 to 500 nm on the surface.
 4. The porous electrospun fiber of claim 1, wherein the acrylamide-based polymer is a crystalline polymer.
 5. The porous electrospun fiber of claim 1, wherein the acrylamide-based polymer has a number-average molecular weight of 5,000 to 500,000.
 6. A method of preparing a porous electrospun fiber comprising the steps of: dissolving an acrylamide-based polymer comprising at least one repeating unit represented by Chemical Formula 1 in an organic solvent to obtain a polymer solution; and performing electrospinning the polymer solution;

In Chemical Formula 1, n is an integer of 15 to 1,800, R is hydrogen or methyl; and R′ is X,

wherein X is —Z—R″; Y is alkylene having 1 to 10 carbon atoms; Z is arylene having 6 to 20 carbon atoms; and R″ is a linear or branched hydrocarbon having 10 to 20 carbon atoms, or a linear or branched perfluorohydrocarbon having 10 to 20 carbon atoms.
 7. The method of preparing a porous electrospun fiber of claim 6, wherein the organic solvent comprises at least one nonpolar solvent selected from the group consisting of n-hexane, cyclohexane, benzene, toluene, chlorobenzene, dichlorobenzene, methylenechloride and 1,-dichloroethan; or at least one polar solvent selected from the group consisting of acetone, chloroform, tetrahydrofuran (THF), dioxane, monoglyme, diglyme, dimethylformamide (DMF), dimethylsulphoxide (DMSO) and dimethylacetamide (DMAC).
 8. The method of preparing a porous electrospun fiber of claim 6, wherein the polymer is dissolved in the organic solvent in an amount of 10 to 40 wt %.
 9. The method of preparing a porous electrospun fiber of claim 6, wherein the electrospinning is performed under the condition of applied voltage of 10 to 30 kV.
 10. The method of preparing a porous electrospun fiber of claim 6, wherein the electrospinning is performed at the electrospinning apparatus comprising a nozzle that has a diameter of 20 to 30 gauge and has a distance of 10 to 20 cm from a fiber collector.
 11. The method of preparing a porous electrospun fiber of claim 6, wherein the electrospinning is performed at a spinning rate of 5 to 20 mL/min. 